<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>类选择器</title>
        <style>
            body{color:red;}
            .one{color:green;}
        </style>
    </head>
    <body>
        body的内容
        <div class="one">
            body下DIV的内容
        </div>
        <span class="one">span的内容</span>
    </body>
</html>